Remote control system



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0; HIS ATTORNEY L. V. LEWIS REMOTE CONTROL sYsTEM Filed March 11, 1939 gw m mmlmmwmw.

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Oct. 21, 1941. L. v. LEWIS REMOTE CONTROL SYSTEM :5 Sheets-Sheet 2 FiledMarch 11, 1939 NQ b N Fl. ma Lm WW1 WQQ HIS ATTORNEY.

Oct. 21, 1941. 1., v. LEWIS REMOTE CONTROL SYSTEM Filed March 11, 1939 5Sheets-Sheet 3 INVENT OR Llagdld 961/65.

H15 A'i'ToRNEY Patented Oct. 21 1941 UNETEQ azsasn ear Y orr 2,259,573REMGTE CGNTRQL SYSTEM Lioyd V. Lewis, Pittsburgh, Pa., assignortof'lhcUnion Switch & Signal Company, Swrssvala. Pa, a corporation ofPennsylvania Application March ll, 1939, Serial No.126L241 (iJl.177--353) 9 @laims.

My invention relates to remote control systems, and more particularly tothe communication or line circuits for such systems.

My invention is particularly adapted for though in no manner limited tocentralized trafno control systems for railroads in which a traindispatchers office or other suitable point of control is connected witha plurality of field stations by line wires, over which code signals aretransmitted at times for controlling selected devices at the stations,and at other times for indicating the condition of station devices atthe ofiice.

My inventionis an improvement upon the centralized trafiic controlsystem disclosed in my pending United States application, Serial No.600,786, filed March 23, 1932, for remote control systems, whichcorresponds with the United States Letters Patent No. 2,229,249, issuedJ anu any 21, 1941.

One object. of my invention is to provide additional communicationchannels over the line wires of the centralized traflic control system,the additional channels being suitable, for example, either fortelephone communication, or for code signaling, or for both purposes. Aspecific object of my invention is to so arrange the systern of my priorapplication that it may be used in connection with a normally open, orbridged line circuit.

A further object of my invention is the provision of an arrangement ofapparatus which will permit, the line circuit of the centralized trafficcontrol system to be used by other codesystems employing difierentnodes, without interference, even though two or more codes are initiatedsimultaneously.

In the specific embodiment herein illustrated, the code system of myprior patent hereinbefore referred to is so modified that the linecircuit is rende ed available for voice frequency communication and alsofor code signaling by means of selector systems of the code wheel type,such systems being well known, as shown, for exempie, in the FieldPatent No. 1,3 l3,256 or in the Gill Patent No. 1,070,301.

Other objects, purposes and features of my in vention will be pointedout as the description proceeds.

I shall describe one form of apparatus embodying my invention and onemodification thereof, and shall then. point out the novel featuresthereof in claims.

Referring to the accompanying drawings, Fig. 1 illustrates the linecircuit for a centralized traffic control system and associatedapparatus :IR

arranged in accordance with one form of my invention, while Fig; 2illustrates an alternative form of apparatus suitable for-use atanintermediate fieldst'ation in the system of Fig. 1. Figs. 3 and 4 showthe local circuits at the ofiice and station, respectively, for thesystem ofrny invention, these circuits being'generally similar to thoseof my Patent No. 2,229,249, hereinbefore referred to, except that ashere shown they have been arranged in a more condensed form and havebeen modified to conform with Fig. l.

Similar reference characters refer to similar partsin each of the twoviews.

Referring to Fig. 1, the reference characters Y, Z designate the linewires of the system which extend from the point'ol control, usually atrain dispatchers cilic'e, as indicated by the legend Oflice on thedrawing, through each of a plurality. of field stations of thecentralized trailic control system, in turn. Since the field stationsare generally similar, but one is shown in order to simplify thedrawings, this being identified on the drawing by the legend CTCStation.

(The line circuitsare'arranged as shown in the Field patent hereinbeforereferred to in that the telephone and code signaling apparatus arebridged across the line wir'es' Y, Z. As shown, a Voice frequencycommunication channel extends from the telephone apparatus 19 at theoffice through a high pass filter illustrated as the condensers 25 toline wires Y, Z thence through slinilarcondensers 2c and telephoneapparatus It at the distant end of the line, as shown on the drawing, orthrough a jack 24 to telephone apparatus, not shown, at an intermediatepoint such as at one of the field stations. The selector apparatus isalso arranged as shown in the Field patent, and this comprises aplurality of code wheels d9, 93 at the ofiice, each of which whenmanually wound up and released makes one revolution during which a codesending relay St is energized over a circuit including the code wheel 89or- 90 and contact 96 to connect a line battery through the contacts ofa pole changer relay 8?, a low pass filter l8 and choke coils l1, to theline wires Y, Z. As the code wheel rotates, relay 8'! isintermittentlyenergized over a circuit including contacts 95, Q1 inaccordance with the arrangement of the code wheel teeth to deliver acode of direct current impulses of alternately reversed polarity to theline wires Y, Z. These impulses selectively control the codewheelselectors 72 which are located as required at different points along theline. Since all the selectors are similarly arranged, but one is shownin order to simplify the drawings, this being lo cated at a pointdesignated Selector station on the drawing.

Each selector [2 is connected across the line in the usual mannerthrough a condenser 14 and a choke coil l1, and may be used to operate acall bell 16, a stick relay F, or for other purposes. The relay F, forexample, may be used to govern railway traflic apparatus as shown forthe similar relay F in the Wallace Patent No, 1,650,575.

The remaining relays of Fig. l are a part of my centralized trafficcontrol system, as shown in detail in Figs. 2 and 3 and with theexception of the added relay V these relays bear the same designation asthe corresponding relays of my patent hereinbefore referred to and thepurposes and detailed mode of operation of these relays and of thecoding units which they control may be ascertained from the patent.

The circuits of the system as arranged in accordance with the presentinvention differ, however, in a number of respects from those of thepatent and these differences will now be explained.

The relays OR and R are the line relays of the system which controlcoding units for selectively receiving code signals from the line andfor also governing the operation of the relays OT and T, which are thetransmitting relays for delivering code signals to the line. In thepatent, a normally closed line circuit is used which includes thewindings of the line relays OR and R and back contacts of thetransmitter relay OT and of the master relay M at each station, all inseries. This arrangement has been changed in accordance with the presentinvention and in Fig. 1 and likewise in Figs. 2 and 3 the line relays ORand R, which are to be understood as being high resistance biased polarrelays, are bridged across the line through choke coils H for preventingthe diversion of voice frequency currents through the relays, and thetransmitter contacts are the normally open front contacts of the relaysOT and T which are bridged across the terminals of the line relays, andtherefore across the line, through low-pass filters l8 which limit therate of change of the code signaling currents to values below the voicefrequency band. As in the patent,

each line relay R controls two slow release relays r LI and L2 which inturn control a third slow release relay LB. For an understanding of thepresent invention it is believed to sufiice to point out that all theserelays are normally deenergized, but that as long as the line relay R isintermittently operated by code signals one or the other of the relaysLl or L2 will remain picked up, that relay LB remains picked up for theduration of the code, and that the ofiice relays OLI, L2 and OLB aresimilarly governed by relay OR. Furthermore, relays OLI and LI are thelast to release at the end of a code, and serve to interpose a pause toproperly space two successive codes. Since the line circuit is normallyopen, the codes are reversed with respect to those of the patent, thatis, in the present instance the line open condition corresponds to theline closed condition in the codes of the patent, and vice versa, and itwill be seen by comparison with the patent that the connections of theline relay contacts to the relays of the coding unit are correspondinglyreversed.

Each code delivered to the line wires Y, Z by a transmitter relay OT orT consists of a series of either '7 or 8 impulses, each of which may berelatively short or long, the intervening line open intervals also beingrelatively short or long to characterize the code.

One feature of the present invention relates to the means for preventinginterference between different codes, and the manner in which this isaccomplished will now be pointed out.

As explained in the patent, a control code for governing the railwaytraffic control apparatus at a selected field station of the CTC system,in accordance with the positions of the corresponding control levers atthe office, is initiated by picking up a start relay identifying thecode to be transmitted, such as relay 234ST, Fig. 3, to complete acircuit for the office master relay OM, which circuit may be traced inFig. 1 from one terminal B of a suitable source of current over a frontcontact of the start relay, back contacts of relays OLI and 0L2 throughrelay OM to the other terminal C of the same source. In the form of theapparatus disclosed herein, relay OM upon be coming energized connectsthe line battery to the contacts of the office transmitting relay OT.Relay OM completes circuits, as shown in Fig. 3, for intermittentlyenergizing relay OT to deliver the desired code to the line wires Y, Zto operate the line relays OR and R. The apparatus at the ofiice and atone station only responds selectively to such code by closing variouscircuits shown in Figs. 3 and 4 to pick up a selector relay such as 234sat the office and a similar relay S at the selected station and thenother relays controlled by relay S are controlled in accordance with thecondition of control levers associated with relay 234s. The firstimpulse delivered to the line by relay OT by energizing relay OR effectsthe successive energization of relays OLl, 0L2 and OLB, the latter relaycompleting a stick circuit extending to terminal B, for holding relay OMenergized for the duration of the code. The stick circuit for relay OMhas been modified as shown herein by including a back contact of thecode sending relay 86 of the selector system.

The circuits for relay 86 in Fig. 1 differ somewhat from those of thecorresponding relay of the Field patent. Thus in Fig. l, relay 86 has apick-up circuit extending from terminal B, back contacts of relays OLI,0L2 and 85, code wheel 89 or 90, contact 9G, relay 85 to terminal C,which is closed upon the release of the code wheel only if no code isthen being delivered to line relay OR so that relays OLI and 0L2 areboth deenergized. Relay 86 upon becoming energized completes a stickcircuit extending to terminal B over its own front contact which isindependent of relays OLI and 0L2 and which is opened at contact 96 uponthe return of the code wheel to normal at the end of the code deliveredby the pole changer Bl.

It will be apparent from the foregoing that neither the release of acode wheel nor the operation of a start relay at the office is effectiveto initiate a code unless relay OR has been deenergized for a timesufficient to effect the release of relay OLI, indicating that the lineis free, while if both systems are initiated at the same time, theselector system takes precedence, relay OM of the CTC system beingreleased upon the energization of relay 8B of the selector system.

Considering now the apparatus at the CTC station of Fig. 1, it is to beunderstood that an indication code, that is, a code indicating a changein the condition of the railway traffic governing devices at thestation, is initiated by energizing a station start relay such astherelay'S-T of Fig. 4

to complete a piclnup circuit for the master relay M.

Relay M, upon becoming energized, at its upper front contact completes acircuit for a vibrator relay V, Fig. 1, and since this circuit includesalso a back contact of relay V, that relay is caused to vibrate to closeits front and back contacts alternately as long as relay M remainsenergized, that is, for the duration of the code. The upper contacts ofrelay V connect terminal B of the local direct current sourcealternately to the two end terminals of the primary Winding of thestep-up transformer i2 which-has its midpoint connected to the otherterminal C of the direct current source, causing current impulses ofalternately opposite polarity tobe impressed upon the primary so that arelatively high 'alternating current voltage of a frequency the same asthe rate of vibration of relay V is developed across the secondaryterminals of transformer l2. This voltage is rectified by the operationof the lower contacts of relay V, andthe resulting rectifiedcurrentisdelivered to the terminals BH and CH and thence over contacts of relayM to ,v the code transmitting contacts of relay T. Relay V andtransformer 12 thus provide a relatively inexpensive and convenient,local source of line current which is generated only when needed,avoiding the necessity for providing a high volte line battery such as-85 at each field station. Relay M, upon becoming energized, completescircuitsas shown in Fig. 4. for intermittently energizing relay T todeliver an indication code to line .wires Y, Z through the low-passfilter l8 and choke coils ll, this code operating the line relays OR andR, but as explained in the patent, only the coding units at the oiiiceand at the transmitting station respond selectively. At the ofiice, aselector relay such as 23% becomes energized, and likewise relay S atthe transmitting station, these relays controlling the operation ofindication devices at the ,ofiice in accordance with conditions at thestation.

Relay R at the transmittingstation governs the transmission of the codeby relay T at that station, while relay R at each station effects theenergization of the associated relays Li, L2 and LB. Relay LB at thetransmitting station upon becoming energized completes a stick circuitfor holding relay M energized, which circuit as shown in my patentextends over front contacts of relays M and LB, and also over a backcontact of relay iii which opens to release relay M at the end of thecode. This circuit as shown in Fig. a differs frointhe correspondingcircuit of my patent in that the connection to terminal B is not made atthe contact of relay i i but the circuit includes B over a front contactof relay T and the other extending to terminal B over a back contact ofrelay T and the right-hancl contact of the line relay R. Since relay Tcontrols R, these contacts operate approximately in unison to maintainthe stick circuit for reiay M closed substantially continuously soas tomaintain relay M picked up as long as the code to which relay R respondsis the same as. that delivered to the line by relay '1.

In order to distinguish. between controls and indications, each controlcode is, arranged to begin with a relatively long impulse and eachindication code with a relatively short impulse, the apparatus at eachstation including a relay E which is selectively responsive to a longfirst impulse of a code-and which is required to be energized in orderto condition the station appatwo branches, one extending to terminal along impulse to transmit, will take ratus to respond selectively to thecode. It follows that a code delivered to the linecircuit by anystation, since it begins with a short impulse, will operate thereceiving apparatus at the office but not that at any other station.Furthermore, in the event the ofiice and one or more stations initiatecodes at the same time, current will be maintained on the line by relayOT after relays T have released and consequently. the

event of simulaneous initiation of'codes from the office and one or morestations, and that control codes take precedence over indication codeswhen both are initiated simultaneously. 7 v It may also happen thatacalling key is opera-ted to initiate a selector code-at the same timethat oneor more stations initiate indication codes. I 7

By reference to Fig. "1 or to the Field patent, it will be seen that thecode wheels 89, -90 are arranged to apply current tothe line circuit bythe energization of relay 8%, prior to the transmission-of code impulsesby relay 8?, for an interval similar to a long step of the code. Byreference to Fig. 1 it will be seen that the connections to battery havebeen arranged so that the initial impulse of a selector code is of thesame polarity as the first impulse of a 'CTC code. This impulse isarranged to be long enough to lock out the station transmitters, so thatselector codes take precedence over indication code when both areinitiated simultaneously.

Another-condition to be considered is the mode of operation when two ormore stations initiate indication codes at the same time. When thisoccurs, the transmitter relays T are held in synchronism by theirrespective line relays R as long as the code elements of the dilferentcodes are alike, but since the codes diiier in at least one eleinent,.-astep will be reached which is long in the code delivered byonetransmitter and short in the-code delivered by another. If this occurson a line-cl0sed, or odd-numbered step, the resu t will be the same aswhen it occurs on the first step as above described, and the stationhaving precedence, the master relay M at the other station releasing todiscontinue the operation of the transmitter at that station. If itoccurs on a line-open, or even-numbered step, relay T at the stationhaving a long interval to transmit will remain released after thecontact of relay R at that station is operated to the left by the nextimpulse following the short interval of release of relay T at anotherstation, to release relay M. It follows that a station having a shortline-open interval to transmit takes precedence over one having a longinterval to transmit. In any case, it is evident that but one stationtransmitter will continue in operation to the end of the code and thatbut one code will be delivered to the ofiice at a time, the severalcodes being delivered to the line circuit one at a time in apredetermined order of code superiority, without interference.

A similar arrangement for lockingout the stations of a system employinganormally closed series line circuit is disclosed in the Snavely,

Miller and Jackel application, Serial No. 31,592, filed July 16, 1935,for Remote control systems, now Patent No. 2,183,155, issued December12, 1939.

There remains to be considered the effect of the different codes uponthe receiving apparatus of the CTC system and upon the selectors. In myCTC system, the selection of a station or of an office panel is effectedby a combination of three long and four short steps directly followingthe first step, and each of the remaining five or seven steps may beeither short or long.

The selector code includes only two long steps out of a total of 32 orless. In the Field patent, the total number chosen for illustration is15 but a total of 17 or 2'7 steps is used in practice. The selectors areimmune to ordinary Morse signals because the latter contain more thantwo long steps in any 17 successive steps, and for the same reason theyare non-responsive to the CTC codes. Likewise the CTC receivers arenon-responsive to the selector codes because the latter do not containthree long steps in any group of eight, as required to effect aselection in the CTC system. It follows, therefore, that the totalnumber of codes provided by both systems may be used, withoutinterference,

Another arrangement for preventing interference in the event that thetransmitters at two or more stations are initiated at the same time maybe used in the system of Fig. 1, this comprising an arrangement forsectionalizing the line as in the system of my patent.

This alternative arrangement is illustrated in Fig. 2, and referring tothis view, it will be seen that the line wires Y, Z, which extend to thecontrol office are carried through each intermediate station over backcontacts of the station master relay M to the line wire sections Yl, Zlwhich, it is to be understood, extend to the next station to the right,while at the station most remote from the ofilce they extend to thetelephone apparatus l9 at that end of the line, as in Fig. 1. In orderto maintain the voice frequency communication channel while relay M isenergized, the back contacts are bridged by highpass filters orcondensers 2|, in the manner disclosed in the Baughman application,Serial No. 256,976, filed February 17, 1939, for Remote control systems,now Patent No. 2,208,446, issued July 16, 1940.

When relay M picks up to initiate transmission from the station shown inFig. 2, relay V is intermittently energized to generate direct currentas already described, but in Fig. 2 as long as relay M remainsenergized, this current is supplied from terminals BH and CH over thefront contacts of relay M to the line wires Yl, Zl extending to thestations more remote from the office.

The contacts of the line relays at such stations are operated to theleft, just as if the office apparatus had initiated a code. Sinceterminals BH and CH remain connected to the more remote section of theline for the duration of the code, this section serves as a source ofcode signaling current for the transmitting station, current fromterminals BH and CH being delivered through the filter l8 and thecontacts of relay T to relay R, and also through the choke coils I! toline wires Y, Z and thence to the office, each time relay T becomesenergized. It will be seen that as long as a station is transmitting acode to the Office, the transmitters at the more remote station are heldlocked out by the current delivered to line Wires extending to thesestations by relay M at the transmitting station.

In the event the office and a station initiate codes simultaneously inthe system of Fig. 2, relay E at the first station will becomeselectively energized due to the long first impulse delivered from theofiice as already explained, and relay E at each more remote stationwill become energized due to the similar impulse delivered to line wiresYl, Zl. When relay E at the first station picks up, its front contactsbridge condensers 2! in the line circuit, and the current delivered toline wires Yl, Zl will then be supplied also to line wires Y, Z afterrelay T has released, thereby maintaining the office line relay ORreversed even though the office transmitter relay OT releases, untilrelay M releases. The office transmitter is thus held on the first stepof the code until relay M releases to disconnect the station source ofcurrent from the line circuit. It will be evident from Fig. 1 that relayM will be released by relay E, the circuits for relay M in Fig, 2 beingthe same as in my patent, these circuits having been already explainedin connection with Fig. 1. It will be seen, therefore, that when relay Mreleases, the receivers at the ofiice and at all stations will havecompleted the first step of a control code and are ready to advance tothe second step under the control of the office transmitter relay OT,which is than free to complete the code.

In view of the foregoing description it is believed that it will beapparent that the apparatus will also function properly in the event theoffice and two or more stations initiate codes simultaneously, and thatthe several codes will be transmitted one at a time in a predeterminedorder without interference.

Selectors of the types hereinbeiore referred to are used quiteextensively by the railroads, and there are many train dispatcherstelephone lines in use over which selectors are controlled. Inaccordance with the present invention such circuits are renderedavailable also for the control of centralized traflic control apparatus,rendering installations of the latter commercialy feasible, in manycases, under conditions which otherwise would not be justified onaccount of the relatively large cost of the line wires if a separateline circuit were required.

In many instances the office equipment of the CTC system will not bedirectly under the control of the train dispatcher or operator whomanipulates the selector calling keys, but will be in charge of adifferent operator. In such cases it is desirable to indicate bysuitable means adjacent the calling keys when the line is free so that acalling key will not be operated when the line is in use. To this end Iprovide a normally energized indicator lamp IE adjacent the selectorcalling keys which is controlled over back contacts of relays CL! and0L2 as shown in Fig, 1. This lamp will be extinguished when ever a codeis being delivered to the line circuit either by the CTC apparatus or bya calling key. In order to definitely inform the operator of thedelivery of a selector code to the line circuit, I provide a second lamp2E which is controlled by relay 86 so as to be lighted only while aselector code is being transmitted.

Although I have herein shown and described but one form of my inventionand one modification thereof, it is understood that various changes andmodifications may be made within the scope spasms of the appended claimswithout departing from the spirit and scope of my invention. 7 Havingthus described my invention, what I claim is: 1 I

1. In a'remote control system, an office and a plurality of stations, anormally deenergized master relay at each station, a normally open linecircuit extending from the oflice through said stations and includingback contacts of the master relay at each station, local sources of linecurrent at each station, means effective when the master relay at anintermediate station is energized to supply steady current from thesource at said station to the line circuit portion extending to moreremote stations and to also supply current from said source interruptedin accordance with a code to the line circuit por tion extending to theoffice, and means for energizing said master relay for the duration orsuch,

code effective only when the line circuit at such station isdeenergized.

2. Remote controlling apparatus comprising a single line circuitconnecting a plurality of stations, a line relay at each stationconnectedtacross said line circuit, a normally open code transmittingcontact and a local source of' line current at each station, means ateach station effective only if the line relay at such station isdeenergized for at times connecting said local source across said linecircuit through said code trans mitting contact and for disconnectingthe portion of said line circuit extending beyond said station, andmeans for steadily energizing said portion as long as it remainsdisconnected.

3. Remote controlling apparatus comprising a single line circuitnormally'ccnneoting an office and a plurality of stations, a line relayconnected across said line circuit at each station, a local source ofline current and a code transmitting contact at each station, means ateach station eiiective only if the line relay at such 7 station is notenergized for connecting the local source across the line circuitthrough the associated transmitting contact and for disconnecting theportion of the line circuit extending to stations more remote from theoffice, means for subsequently operating said transmitting contact todeliver a code to the remaining portion of said line circuit, means forsteadily energizing said disconnected portion of the line circuit whilesaid code is being delivered, and means for operating upon thecompletion of said code to restore the normal line circuit.

4. In a remote control system, a normally open line circuit extendingfrom an oiiice to a plurality of stations, a normally deenergized linerelay bridged across said line circuit at each station, a local sourceof current and a code transmitting contact adapted to be connected inseries across said line circuit at each station, a master relay at eachstation, a pick-up circuit for each master relay closed only when theassociated line relay is deenergized, a stick circuit for each masterrelay, means effective when each master relay is energized forconnecting said local source across the portion of the line circuitextending to stations more remote from the office and for interposingmeans blocking the flow of current from said source between said portionand the remainder of said line circuit, and means for operating theassociated transmitter contact when such master relay is energized todeliver a code to said oflice.

5. In combination, an office and a station connected by a single linecircuit, a remote conline circuit during mitte'rs including one at saidoifice'an'd one" at said station each operableonly if'initiated-W-henthe'lin'e is free, to deliverimpulse codes to said line circuit,starting means for each transmitter free to be actuated at any timetocondition that transmitterto deliver its code, indication means at theoilice effective for indicating when theline is free, a plurality ofmanually releasable code Wheels at said office, an additional codetransmitter'atsaid oiiice operable immediately in response tothe manualrelease of a code Wheel but only if the code wheel isreleased when theline circuit is'freeg-to deliver other controlled over said linecircuitin response to the first impulse of a code and eiiective to disconnectsaid station transmitter from said line circuit during the transmissionof a code initiated '5 simultaneously and jointly by said stationtransmitter'and by the omcetransmitter of said remote control system orby said additional transmitter, means for disconnecting the oiiicetransmitter of said remote control system from said the transmission ofa code initiated simultaneously and jointly by said ofiice transmitterand said additional transmitter, and storing means associated with eachremote control system transmitter for initiating its operation as soonas the line is free if the starting means for such transmitter isactuated-when the line is in use or if such transmitter has beendisconnectedfrom the line circuit by'the operation of anothertransmitter.

6.- In combination, an oiiice and a station connected by a single linecircuit, a remote control systemhaving a plurality of code transmittersincluding one at said oflice and one at said station each operable wheninitiated, to deliver impulse codes to said line circuit, a plurality ofmanually releasable code Wheels at said office, an additional codetransmitter at said oflice operable immediately in response to themanual release of a code wheel, to deliver other impulse codes to saidline circuit, line relays at said office and at said station, means forinitiating each code transmitter to deliver its code effective only whenthe line is free as manifested by the condition of the associated linerelay, means for interrupting the transmission of a code by thetransmitter at said station when the response of the associated linerelay is not in accordance with the character of the first element ofsuch code, means for interrupting the transmission of a code by theofiioe transmitter of said remote control system when said additionaltransmitter is initiated at the same time, and storing means associatedwith the transmitters of said remote control system for storing eachsuch interrupted code for subsequent transmission when the line is againfree.

7. In combination, an oifice and a station connected by a normally openline circuit, a remote control system having a control code transmitterat said oiiice operable when initiated to deliver impulse codes to saidline circuit in each of which the first impulse is relatively long, andalso having an indication code transmitter at said station operable wheninitiated to deliver impulse codes to said line circuit in each of whichthe first impulse is relatively short, a plurality of manuallyreleasable code Wheels at said office, an additional transmitter at saidofiice adapted to be initiated in response to the manual release of acode wheel to deliver an initial relatively long impulse to said linecircuit followed trol system having a plurality of code trans V impulsecodes to said line circuit, interference preventing means t3 aesasve bya code characteristic of the operated code wheel, line relays at saidofilce and station responsive to the code impulses in said line circuit,means for initiating each code transmitter effective only when the lineis free as manifested by the steadily deenergized condition of theassociated line relay, means for interrupting the transmission of a codeby the transmitter at said station in the event the station line relayfails to release in response to the operation of that transmitter forterminating the first impulse of such code, means for interrupting thetransmission of a code by the oflice transmitter of said remote controlsystem when said additional transmitter is initiated at the same time,and means associated with the transmitters of said remote control systemfor storing each such interrupted code for subsequent transmission whenthe line is again free.

8. In combination, an office and a station connected by a single linecircuit, a remote control system having a plurality of code transmittersincluding one at said office and one at said station each operable whenthe line is free, to deliver impulse codes to said line circuit, aplurality of manually releasable code wheels each operable it manuallyreleased when the line is free, to immediately deliver other impulsecodes to said line circuit, interference preventing means effective whena code is initiated by the station transmitter and by the ofiicetransmitter of said remote control system or by a code wheel at the sametime for interrupting the operation of said station transmitter, otherinterference preventing means efiective when a code is initiated by acode Wheel and by the office transmitter of said remote control systemat the same time for interrupting the operation of said o-fi'lcetransmitter, and storing means associated with the transmitters of saidremote control system for storing each such interrupted code forsubsequent transmission when the line is again free.

9. In a communication system having an oflice and at least two stationsconnected by a line circuit, the combination with a remote controlsystem having a plurality of cod-e transmitters including one at saidoflice and one at each station each operable when initiated to deliveran impulse code to said line circuit, and having starting means for eachtransmitter free to be operated at any time to condition suchtransmitter to transmit its code but effective to initiate its operationonly when the line circuit is free, and also having storing meansefiective to maintain each actuated starting means in its actuatedcondition until the corresponding code has been fully transmitted, saidremote control system also including interference preventing meanseffective when two or more transmitters are initiated simultaneously andthey jointly deliver the first impulse of a code to the line circuit, toprevent further operation of all but one during such code, of anadditional transmitter for delivering other impulse codes to said linecircuit, together with manually operable means free to be operated atany time but effective only if operated when the line if free, toinitiate the operation of said additional transmitter, and interferencepreventing means effective when said additional transmitter and one ormore transmitters of said remote control system are initiatedsimultaneously and they jointly deliver the first impulse of a code tosaid line circuit, to prevent further operation of any remote controlsystem transmitter during such code.

LLOYD V. LEWIS.

